Iron

Iron (Fe) is the most widely used metal in the world and one of the most examined elements in 0620. It appears in extraction, reactivity, alloys, catalysis, and rusting.

Where it appears in 0620

Iron shows up across the metals and periodic-table topics:

• Extraction of metals: the blast furnace is the set-piece reduction, examined for raw materials and the three key equations.
• Transition elements: iron demonstrates coloured compounds, variable oxidation states (Fe2+ and Fe3+), and catalysis.
• Rusting and prevention: the conditions for rusting and the methods to stop it.
• Alloys and uses: iron is alloyed into the many forms of steel.
• Tests for ions: Fe2+ and Fe3+ give differently coloured precipitates with sodium hydroxide.

Position in the periodic table

• Symbol: Fe (from Latin ferrum)
• Atomic number: 26
• Transition metal, Period 4
• Electron configuration: 2, 8, 14, 2

As a transition element, iron forms coloured compounds, has variable oxidation states (Fe2+ and Fe3+), and acts as a catalyst.

Physical properties

Property	Value
Melting point	1538 C
Density	7.87 g/cm3
Appearance	Silver-grey, lustrous
Conductivity	Good conductor of heat and electricity
Magnetic	Yes — ferromagnetic

Extraction: the blast furnace

Iron is extracted from its ore (haematite, Fe2O3) by reduction with carbon monoxide in a blast furnace.

Raw materials

Material	Purpose
Iron ore (Fe2O3)	Source of iron
Coke (C)	Fuel; makes the CO reducing agent
Limestone (CaCO3)	Removes acidic impurities (SiO2) as slag
Hot air	Provides O2 for combustion

Key equations

1. C(s) + O2(g) -> CO2(g) (coke burns)
2. CO2(g) + C(s) -> 2CO(g) (carbon dioxide reduced to carbon monoxide)
3. Fe2O3(s) + 3CO(g) -> 2Fe(l) + 3CO2(g) (iron ore reduced)

The iron ore is reduced (oxygen removed); carbon monoxide is the reducing agent. Limestone removes the sandy impurity: CaCO3(s) -> CaO(s) + CO2(g), then CaO(s) + SiO2(s) -> CaSiO3(l) (slag).

Reactivity

Iron sits in the middle of the reactivity series, below zinc and above hydrogen.

• With dilute HCl: Fe(s) + 2HCl(aq) -> FeCl2(aq) + H2(g) (slow; pale green solution)
• With dilute H2SO4: Fe(s) + H2SO4(aq) -> FeSO4(aq) + H2(g)
• With steam: 3Fe(s) + 4H2O(g) -> Fe3O4(s) + 4H2(g) (reversible; iron glows red)
• With copper(II) sulfate: Fe(s) + CuSO4(aq) -> FeSO4(aq) + Cu(s) (displacement — iron is more reactive)

Rusting and prevention

Iron rusts only when exposed to both oxygen and water. The product is hydrated iron(III) oxide, Fe2O3.xH2O.

Prevention: painting, oiling, greasing, plastic coating, galvanising (zinc coating), sacrificial protection, and alloying (stainless steel with chromium). See rusting and prevention.

Alloys

Alloy	Composition	Properties and uses
Mild steel	Fe + ~0.25% C	Strong, malleable; car bodies, girders
High carbon steel	Fe + ~1.5% C	Hard, brittle; cutting tools
Stainless steel	Fe + Cr + Ni	Corrosion-resistant; cutlery, surgical instruments

Alloys are harder than pure metals because atoms of different sizes disrupt the regular lattice, stopping the layers sliding.

Iron as a catalyst

• Haber process: iron catalyses N2 + 3H2 ⇌ 2NH3
• Catalysis is typical of transition elements

Compounds and colours

Ion	Colour	NaOH test
Fe2+ (iron(II))	Pale green	Green precipitate of Fe(OH)2
Fe3+ (iron(III))	Orange-brown	Red-brown precipitate of Fe(OH)3

See tests for ions.

Key facts at a glance

Fact	Detail
Symbol	Fe
Proton number	26
Position	Transition element, Period 4
Oxidation states	Fe2+ (green) and Fe3+ (orange-brown)
Extraction	Blast furnace, reduced by carbon monoxide
Key use	Alloyed into steel

Common exam mistakes

• Naming carbon as the reducing agent in the furnace. The main reduction of the ore is done by carbon monoxide (CO), not carbon itself: Fe2O3 + 3CO -> 2Fe + 3CO2.
• Giving only one condition for rusting. Rusting needs both water and oxygen. Salt speeds it up but is not required.
• Confusing the iron hydroxide colours. Fe(OH)2 is green (from Fe2+); Fe(OH)3 is red-brown (from Fe3+) — and the formulae must match the ion charge.
• Using Fe3+ in the displacement equation. When iron displaces copper it forms Fe2+: Fe -> Fe2+ + 2e-, giving FeSO4.

Exam-style questions

Describe how iron is extracted from haematite in the blast furnace. Include the two equations that produce and then use the reducing agent. (4 marks)

Mark scheme

• coke burns in the hot air: C + O2 -> CO2 [1]
• carbon dioxide reacts with more coke to make carbon monoxide: CO2 + C -> 2CO [1]
• carbon monoxide reduces the iron(III) oxide: Fe2O3 + 3CO -> 2Fe + 3CO2 [1]
• molten iron runs to the bottom of the furnace / the ore is reduced as oxygen is removed [1]

Examiner note: the reducing agent is CO — an answer that has carbon reducing the ore directly loses the key reduction mark.

An iron nail is left in copper(II) sulfate solution and becomes coated in copper while the solution fades. Explain what happens and write an ionic half-equation for the change to the iron. (3 marks)

Mark scheme

• iron is more reactive than copper, so it displaces copper from the solution [1]
• Fe + CuSO4 -> FeSO4 + Cu (copper deposits on the nail) [1]
• iron is oxidised: Fe -> Fe2+ + 2e- [1]

Examiner note: the solution fades because blue Cu2+ is replaced by pale green Fe2+ — and iron forms Fe2+ here, not Fe3+.